This connection between the stationary vanes and the outer shroud is usually provided by attachment elements that include threaded portions, such as nut-and-bolt fastener assemblies, as described in document EP 1 801 357.
Nevertheless, there exist certain drawbacks if a threaded bolt is used at the top of a vane and penetrates into an opening in the shroud, where it is held by a nut screwed onto the outside of the shroud. The presence of a screw thread leads to the risk of the thread breaking, there are corresponding fabrication costs, and account needs to be taken of the weight of the nut.
In addition, other problems are encountered when using known techniques for mounting by welding.
Thus, document U.S. Pat. No. 5,474,419 provides in particular for welding the tops of stationary vanes in openings passing through the outer shroud and presenting a shape that is complementary to the tops of the vanes.
However, in order to achieve the required strength, it is necessary for the welding that connects the shroud to an end portion of the top of the vane to be performed through the entire thickness of the material of the outer shroud, which, given the welding techniques that can be implemented, necessarily gives rise to a melt bath through the entire thickness of the material of the shroud, thereby giving rise to droplets of material being spattered on the inside face of the shroud, and thus in the air-flow section.
It will be understood that such welding through the entire thickness gives rise to drawbacks, including the following:                deformation of the welded parts, and in particular of the outer shroud;        spattering of droplets of material giving rise, together with the weld bead, to surface discontinuities in the inside face of the outer shroud, thereby disturbing the stream and generating head loss in the air-flow section, such that in order to remove these surface discontinuities it is necessary to take further action on the assembly made up of the outer shroud and the welded stationary vanes, which action is complex and gives rise to additional fabrication costs, and can also give rise to other mechanical defects on those parts;        strict fabrication tolerances are necessary for complying with the dimensions and the positioning of the openings in the outer shroud; and        fabrication difficulties associated with the complex shape of the end portions of the tops of the vanes and the openings in the outer shroud, with this arising either during the machining of these elements or during the step of welding them together.        